Vehicle fuel systems include evaporative emission control systems designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel.
Purging vapors from the fuel vapor canister may involve opening a canister purge valve coupled to a conduit between the fuel vapor canister and the intake manifold. Over the course of vehicle operation, the canister purge valve may entrap contaminants or other debris originating from components of the fuel system. These contaminants may prevent the canister purge valve from closing completely.
Diagnostic routines may be intermittently performed to test the emission control system for leaks. In a situation where the canister purge valve cannot close completely due to the presence of contaminants, a diagnostic routine is likely to detect the presence of a leak in the system. In some examples, a malfunction indicator light may be actuated following two consecutive diagnostic routines that detect the presence of a leak. The inventors herein have recognized that there is an opportunity to clean the canister purge valve following the first positive leak detection and prior to the second diagnostic routine.
In one example, some of the above issues may be addressed by a method for a fuel system coupled to an engine, comprising: under predetermined engine operating conditions, opening a canister purge valve; and while maintaining the canister purge valve open, pulsing a canister vent solenoid valve open and closed one or more times to generate pressure pulsations in a conduit coupled to the canister purge valve. By pulsing the canister vent solenoid valve in this way, it may be possible to dislodge debris in the valve (such as at a valve seat) so that the valve can once again fully seal. For example, the pulsing may be in response to a potential leak being identified in the system. If the pulsing can dislodge the debris so that a subsequent check confirms that there is no leak, then a diagnostic code indicating degradation is not set. However, if after the pulsing a leak is still detected, then the code is set.
In another example, some of the above issues may be addressed by a method for cleaning a fuel vapor canister purge valve, comprising: under vacuum conditions, opening the fuel vapor canister purge valve, and generating pressure pulsations in a conduit coupled to the fuel vapor canister purge valve by opening and closing a fuel vapor canister vent valve one or more times while maintaining the fuel vapor canister purge valve open.
In still another example, a fuel system for a vehicle, comprising: a fuel tank for storing fuel used by a vehicle engine, a fuel vapor canister coupled to the fuel tank for receiving and storing fuel tank vapors, a fuel vapor canister purge valve coupled between the canister and an engine intake manifold for delivering stored fuel tank vapors from the canister to the engine, a fuel vapor canister vent solenoid valve coupled between the canister and atmosphere, and a controller including computer readable instructions for, in response to a manifold absolute pressure being higher than a threshold during engine running, opening the fuel vapor canister purge valve for a predetermined duration, while maintaining the fuel vapor canister purge valve open, pulsing the fuel vapor canister vent solenoid valve open and closed one or more times to generate pressure pulsations in a conduit coupled to the canister purge valve.
In one example, when the manifold absolute pressure is above a threshold, sufficient vacuum may exist to flush loose contaminants and/or debris into the engine intake system. By opening the canister purge valve, then subsequently pulsing the canister vent solenoid valve open and closed, pressure pulsations may be created in conduits coupled to the canister purge valve. In this way, contaminants and/or debris that may prevent the canister purge valve from closing completely may be dislodged and evacuated to the intake manifold. This in turn, may allow the canister purge valve to close completely, mitigating a potential leak source. This may be accomplished without a malfunction indicator light being actuated, which may in turn prevent unnecessary and costly diagnostics and maintenance from being carried out.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.